This invention relates to rotating machines wherein a first rotating member is maintained in close physical relationship to a second fixed or rotating member and more particularly to a method and apparatus for thermally controlling the setting between the first and second members. While the invention is thus broadly applicable, it will be disclosed more fully with reference to the printing art to which it is particularly applicable.
For modern printing operations, a web of paper is fed into a printing press where it is passed between a pair of cylinders which print ink images on one or both sides of the web. In an offset press, which is selected as being representative of printing presses to which the present invention can be applied, these printing cylinders are called blanket cylinders. The blanket cylinders are precisely supported for rotation in a rigid frame which maintains a firm pressure or loading between the cylinders. The ink images are transferred to the blanket cylinders by plate cylinders via techniques well known in the art and un-important to the present invention.
Printing and ink transfer surfaces or plates of the blanket and plate cylinders respectively are clamped thereto by clamps positioned in slots or gaps which run the entire lengths of the cylinders. The positioning of the gaps and the synchronized rotation of the cylinders insures that the gaps come together or meet one another at common contact zones which are free of images to be printed. The meeting of the gaps as the cylinders pass through the common contact zones tends to cyclically change the loading on the cylinders, particularly the loading between the blanket cylinders which engage the paper web. That is, since the gaps are effectively flattened sections on the cylinders, the cylinders are somewhat unloaded as the gaps meet and pass by one another.
The repetitive load changes on the cylinders lead to rhythmic vibrations in the printing press. These vibrations can lead to inking problems which appear as streaks across pages printed on the press and are generally encountered as the speed of the press is increased toward the maximum.
A significant factor in the occurrence of streaking, particularly at higher press speeds, is the tendency of the cylinders to bow during operation. As the cylinders rotate, centrifugal force causes their effective radius to grow slightly, thereby increasing the loading between adjacent cylinders. The increased loading owing to centrifugal growth in turn greatly increases the frictional heating of the cylinders where they contact, which further increases the loading due to thermal expansion of the heated portions of the cylinders. Since the cylinder journals are fixed with regard to one another in the frame of the press during operation, bowing of the cylinders may result as the cylinders tend to push apart at the points where they contact while the ends of the cylinders are fixed relative to the frame.
In addition to the possibility of streaking, the existence of centrifugal growth in the rotating cylinders with the attendant increase in loading may have other undesirable effects. Uneven dot and line resolution in the printed web along the width of the blanket cylinders may result from an increased loading of the cylinders at their ends with a simultaneous decrease in loading toward the middle. Increased frictional heating of the blanket cylinders near their ends may dry out dampening solution in the paper web, leading to "scumming" or unclean looking print in the drier areas of the web. Further, continued overloading of the cylinders may shorten the useful life of the cylinder bearings and the cylinders themselves, requiring a premature replacement of the bearings and/or cylinders--a costly and time consuming operation.
In the past, such problems have been attacked by stiffening the cylinders or by making the cylinders larger and heavier. However, these efforts have been only marginally successful to allow somewhat higher press operating speeds before streaking and other print deficiences occur.
After the web of paper has been printed, it is passed to various other machines, for example to a dryer and/or a chill roll device, before it is cut and folded, sheeted or otherwise further processed. Rotary cutters or perforators are generally used to sever or punch the webs of paper moving through the printing machinery to produce or define individual sheets along the web and/or to trim away waste.
Rotary cutters and perforators are generally constructed by providing for the rotation of a first member having one or more cutting surfaces, punches or perforators which are disposed relative to a second member to sever or punch a paper web moving between the two members as the first member is rotated. The second member may be a fixed knife or anvil having a single cutting surface past which the cutting surfaces of the first member are rotated. The second member may also be rotated and comprise a rotary knife or anvil. A rotary anvil would have a hardened outer cylindrical surface to interface with the cutting surfaces of the first member. Multiple cutting surfaces provided on the rotating first member are spaced about the circumference of the circle traced by rotation of the cutting surfaces to form sheets of equal sizes or to trim away waste portions of the web.
In any event, the spacing between the first member and the second member must be carefully and precisely set to both obtain a proper cut or perforation of the paper web and to avoid damage to the cutting surfaces. Accordingly, both members are supported at their ends in a single rigid framework which provides bearing surfaces for rotating members and permits adjustment of the members relative to one another. Such adjustment is typically made by jacking screws, shims or by eccentric adjustment apparatus such as disclosed in U.S. Pat. No. 4,171,655.
An operator precisely sets the rest position of the members relative to one another so that precise cuts or perforations of the web are made. Such static setting of rotary cutters and perforators is adequate for relatively low speed operation. However, this setting will often change during operation. On one hand, as the speed of rotation increases to higher and higher speeds, such as is possible with improved technology in associated equipment such as printing presses, the setting between the members will change due to centrifugal force which tends to cause the effective radius to the cutting surface(s) of the rotating member (or members) to increase or "grow". This tends to reduce the clearance between the cutting surfaces. On the other hand, wear tends to reduce the effective radius of the members which tends to increase the clearance. In recently set cutters/perforators, the growth tends to cause the cutting surfaces to grow closer and closer to one another and ultimately may result in contact which can dull the cutting surfaces or even lead to breakage. Since the wear and growth bear no correlation to one another, they therefore do not compensate for each other and the quality of the cut made by the rotary cutter/perforator is impaired with both increased speed and lengthy operation.
Available mechanical adjustments of the settings of the members relative to one another are complex and/or require continuous manual adjustment. Such adjustable setting arrangements are both time consuming, potentially inaccurate and are not easily adaptable to existing rotary cutters/perforators.